In 3GPP, studies are being made on “ETWS (earthquake and tsunami warning system)” for distributing emergency information such as information on earthquakes, tsunamis and the like.
As shown in FIG. 1, in “ETWS,” a certificate authority system 2 is configured to attach an electronic signature to emergency information received from an emergency information provider system 1, and to report the emergency information by a CBS (cell broadcast service) message or the like to cells included in the area where the earthquake or the like has occurred.
However, the above-mentioned “ETWS” has a problem that it is difficult to prevent a “forwarding attack” in which a malicious third party forwards emergency information received in the area where the earthquake or the like has occurred, to a mobile station in a different area (area where no earthquake or the like has occurred) to cause confusion.